In such an X-ray device, the inverter usually generates a DC voltage from a network AC voltage in an intermediate circuit, said DC voltage being inverted by means of an inverse rectifier into a higher frequency AC input voltage for the high voltage generator. By means of a transformer and a rectifier, for example, the high voltage generator then generates the high voltage required by the X-ray tube in the order of magnitude of about 100 kV. The X-ray tube in the X-ray device is used, for example, to generate radiation for medical applications, in particular in a computer tomography scanner.
In a medical X-ray device in particular, spatial separation of the inverter from the high voltage generator or from the X-ray source is desirable since cumbersome equipment in the vicinity of the X-ray source would restrict the access required when taking an angiogram, for example. This particularly applies to a computer tomography scanner where the X-ray source rotates around the patient and consequently the energy has to be supplied by a fixed system.
If the high voltage generated by the high voltage generator is supplied to the X-ray source in known proportions over circuits of a corresponding length, this results in high capacitors in the high voltage circuit which cause interference when using pulses, because large amounts of energy are stored. Disadvantageously, this leads to an exposure of the patient to radiation that is unnecessary because no image is generated. Furthermore, in the event of collision ionization in an X-ray tube, the stored energy leads to considerable interference with the electronic systems located in the vicinity. If the high voltage is supplied to the rotating gantry of a computer tomography scanner via slip rings, then the volume of air required for the isolation of the high voltage is very considerable, which involves a considerable disadvantage in terms of costs.
Alternatively, it is known for the network AC voltage or for a DC voltage generated for this purpose for the intermediate circuit to be supplied to the rotating system by means of slip rings. However, this presents the problem already mentioned in the introduction that the further components required to generate the high voltage also have to be mounted on the rotating system, which results in considerable outlay in order to achieve mechanical stability because of the bulk and volumes involved, particular at high rotation speeds.
U.S. Pat. No. 4,969,171 discloses an X-ray device of the kind mentioned in the introduction, in which device, at the output end, the AC input voltage of the inverter is transmitted from the stationary end via slip rings to a rotating high voltage generator. In such a transmission of the AC input voltage, there disadvantageously occurs a not inconsiderable emission of electric and magnetic fields by the lines from the output of the inverter to the slip ring, which can have a negative influence on the electronic systems in the vicinity. A further disadvantage in such a transmission is that the power that can be transmitted and the length of the permissible transmission line from the inverter to the high voltage generator are limited by the frequency of the AC input voltage. This is because, depending on the frequency, voltage drops or transmission losses occur as a result of the inductances and loss resistances present in the lines.